Powders of silica-oxide and mixed silica-oxide and method of preparing same

ABSTRACT

Silica powders and mixed silica-oxide powders and methods of preparing such powders for use as catalyst supports for polymerization processes.

This application is a Divisional of Ser. No. 09/060,340, filed on Apr.14, 1998, now U.S. Pat. No. 6,107,236.

FIELD OF THE INVENTION

This invention relates to silica powders and mixed silica-oxide powdersand methods of preparing such powders for use as catalyst supports forpolymerization processes.

BACKGROUND OF THE INVENTION

The use of amorphous gels and precipitates as support material forpolymerization catalysts is known. For example, aluminophosphate gelsand precipitates have often been used for such support materials. Insome cases, the support was improved by incorporating silica into thealuminum phosphate support.

While aluminophosphates have long been known, along with their methodsof preparation, such aluminophosphates have not as yet achievedcommercial success. Part of this is believed to be that the prior artaluminophosphates lacked a combination of physical properties which havebeen found to characterize superior polymerization catalysts. It is thecombination of a high macropore volume of at least 0.1 cc's per gramplus a fragmentation potential (to be defined below) of preferably 30 to60 plus a preferred mesopore volume of 0.3 to 0.8 cc's per gram whichparticularly characterize the superior polymerization catalysts. In twoprior inventions of Applicants (Pecoraro and Chan, U.S. patentapplication Ser. No. 08/742,794 U.S. Pat. No. 6,022,313; Auburn andPecoraro, U.S. patent application Ser. No. 08/741,595 U.S. Pat. No.5,869,587), which are incorporated herein by reference, a newaluminophosphate with both high macropore volume and a fragmentationpotential about 30 was developed which was also both physically andthermally stable. It is believed that the presence of sheets ofaluminophosphate in the microstructure results in the packing of themicrostructures in such a way that a high macropore volume and a highfragmentation potential are achieved along with physical and thermalstability.

In another related invention by Applicants (U.S. application Ser. No.08/961,825 U.S. Pat. No. 6,111,037, Auburn, Pecoraro and Chan), which isa continuation-in-part of Ser. Nos. 08/741,595 and 08/742,794 discussedabove, and which is also incorporated by reference herein, asilica-modified, amorphous aluminophosphate composition which like theprevious inventions exhibits a microstructure of sheets and exhibitsspheres of silica-modified aluminophosphate as well.

The use of silica alone or the combination of silica with other oxidessuch as alumina or titania or vanadia to form such amorphouscompositions for use as polymerization catalyst support material is alsoknown. Previously, the microstructure of such supports primarilycontained small particles. As a result of this small particle structure,it was difficult to tailor the materials over a wide range of poresizes, distributions and volumes, and of acceptable fragmentationcharacteristics.

It would be desirable to find silica support materials which could beused over a wide range of pore sizes, distributions and volumes and ofacceptable fragmentation characteristics.

The present invention has achieved such materials. The present inventionhas achieved high surface area, amorphous silicas which surprisinglyform a continuous network matrix, rather than the typical smallparticles found in conventional amorphous silicas. Furthermore, the poresize and the distribution and volume of the pore size can be tailoredover a wide range.

Surprisingly, also, the present invention achieves an amorphous SiO₂base composition with a non-particulate, dense, network matrix andencapsulated less dense, non particulate regions with true macropores.In one embodiment, the present invention also comprises a sheet-likemicrostructure.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an amorphous SiO₂ ormixed oxide silica base composition comprising:

(a) a non-particulate, dense, continuous network matrix; and

(b) encapsulated, less dense, non particulate regions with truemacropores.

Another object of the present invention is to provide such an amorphousSiO₂ or mixed oxide silica base composition in which the gel matrixfurther comprises a sheetlike microstructure.

Still another object of-the present invention is to provide such anamorphous SiO₂ or mixed oxide silica base composition in which thecomposition has surface areas in a range of from 150 to 600 m²/gm.

Yet another object of the present invention is to provide such anamorphous SiO₂ or mixed oxide silica base composition in which thecomposition has a mean mesopore diameter in a range of from 60 to about250 Å.

An additional object of the present invention is to provide such anamorphous SiO₂ or mixed oxide silica base composition in which thecomposition has a measured pore volume in a range of from about 0.5 to1.5 cc/gm.

Still another object of the present invention is to provide such anamorphous SiO₂ or mixed oxide silica base composition in which thecomposition has a macropore volume of at most 0.5 cc/gm.

Yet another object of the present invention is to provide an amorphousmixed oxide silica base composition selected from the group consistingof silica alumina, silica titania, silica vanadia and silica zirconia.

An additional object of the present invention is to provide powdersproduced from such an amorphous SiO₂ or mixed oxide silica basecomposition.

A further object of the present invention is to provide such powderswhich are spray dried.

Yet a further object of the present invention is to provide such powderswhich are vacuum dried.

Still a further object of the present invention is to provide such spraydried powders having fragmentation potentials in a range of from about20 to about 30.

Another object of the present invention is to provide a catalystcomprising such a SiO₂ base composition, the composition beingimpregnated with a catalytic amount of at least one transitionmetal-containing compound.

Yet another object of the present invention is to provide such acatalyst in which the at least one transition metal-containing compoundis a chromium compound.

Still another object of the present invention is to provide such acatalyst in which the at least one transition metal-containing compoundis present in an amount of 0.1 weight percent or greater based on thetotal catalyst weight.

An additional object of the present invention is to provide such acatalyst in which the at least one transition metal-containing compoundis present in an amount in the range of from about 0.1 weight percent toabout 10 weight percent.

Yet an additional object of the present invention is to provide apolymerization process comprising contacting such a catalyst with atleast one alpha-olefin under polymerization conditions.

Still an additional object of the present invention is to provide amethod for preparing a silica gel composition which is a precursormaterial for a silica powder material with a microstructure comprising anon-particulate, dense, continuous network matrix and encapsulated, lessdense, non particulate regions with true macropores, the methodcomprising:

(a) forming a first aqueous solution comprising silica ions;

(b) forming a second aqueous solution capable of neutralizing said firstaqueous solution; and

(c) contacting said first and second aqueous solutions in amixer-reactor under mixing conditions to form the silica gelcomposition.

An additional object of the present invention is to provide an olefinpolymerization catalyst prepared from a silica gel composition obtainedby such a method.

Yet another object of the present invention is to provide such a methodin which the first aqueous solution is an acidic solution comprisingsodium silicate and acid and in which the second aqueous solution has apH above 8.

Still an object of the present invention is to provide such a method inwhich the second aqueous solution is an ammonia based material selectedfrom the group consisting of ammonium hydroxide; ammonium carbonate;ammonium bicarbonate and urea.

An additional object of the present invention is to provide such amethod in which the first aqueous solution is a basic solution of sodiumsilicate and in which the second aqueous solution has a pH below 6.

Yet an additional object of the present invention is to provide such amethod in which the second aqueous solution is sulfuric acid.

Still an additional object of the present invention is to provide such amethod, in which the apparent average shear rate in the mixer-reactor isgreater than about 0.5×10⁴ sec⁻¹.

Another object of the present invention is to provide such a method inwhich the neutralization step is conducted in such a manner that the pHof the combined first aqueous solution and the neutralizing medium iscontrolled in the range of about 3.5 to about 11.

Yet another object of the present invention is to provide such a methodin which the catalyst is activated by being heated to a temperature inthe range of 300° C. to 900° C. for from 2 to 16 hours.

Still another object of the present invention is to provide such amethod further comprising the steps of:

(a) preparing an aqueous slurry of amorphous silica gel by continuouslyfeeding an acidic solution comprising sodium silicate and acid to anemulsifier mixer while simultaneously and continuously feeding to saidmixer an alkaline solution;

(b) operating said mixer with sufficient shear so that the precipitatedsilicate has sheets of silica in its microstructure;

(c) recovering said silica from said aqueous slurry using a vibratingfiltration membrane to a solids content from 8 to 20 wt. %, afterwashing;

(d) drying and calcining the silica from (c);

(e) dispensing a chromium compound substantially uniformly onto saidsilica to form a catalyst having from 0.01 to 4 wt. % chromium;

(f) drying said catalyst; and

(g) activating said dry catalyst from (f) by heating to a temperaturefrom 300° C. to 900° C. for from 2 to 16 hours.

Yet another object of the present invention is to provide an olefinpolymerization catalyst prepared by such a method.

Another object of the invention is to provide such a method furthercomprising aging the silica gel composition in deionized water for up toone hour.

Yet another object of the present invention is to provide a method ofpreparing the silica powder composition from such a silica gelcomposition comprising the steps of:

(a) washing the silica gel with solutions of ammonium acetate,bicarbonate or nitrate;

(b) washing the silica gel composition in deionized water to furtherreplace salts-contaminated water in the composition with fresh water;and

(c) drying the washed composition to remove substantially all water.

Still another object of the present invention is to provide such amethod further comprising calcining the dried composition in a fixedfluid bed type calciner for up to 8 hours at a maximum temperature of450° C.

Another object of the present invention is to provide a polymerizationprocess comprising contacting at least one mono-1-olefin having from 2to 8 carbon atoms per molecule under polymerization reaction conditionsin a polymerization reaction zone with a catalyst comprising an activecatalytic component on a silica support comprising (a) anon-particulate, dense, gel matrix; and (b) encapsulated regions withtrue macropores.

Still another object of the present invention is to provide such apolymerization process in which the catalytic component comprises achromium component on the silica support.

Yet another object of the present invention is to provide such apolymerization process in which the at least one mono-1-olefin isselected from ethylene; propylene; butene-1; hexene-1 and octene-1.

An additional object of the present invention is to provide such apolymerization process in which the at least one mono-1-olefin comprisesethylene and from 0.5 to 2 mole percent of one additional mono-1-olefinselected from propylene; butene-1, hexene-1 and octene-1.

A further object of the present invention is to provide a method forpreparing silica alumina powder material with a microstructurecomprising a non-particulate, dense, continuous network matrix andencapsulated regions with true macropores and sheets, the methodcomprising:

(a) preparing an acid aqueous solution comprising aluminum and siliconions;

(b) preparing a basic aqueous solution comprising ammonium hydroxide;

(c) mixing the acidic aqueous solution and the basic aqueous solution ina mixer to obtain a gel slurry with a microstructure comprising anon-particulate, dense, continuous network matrix, encapsulated regionswith true macropores and sheets;

(d) maintaining the gel at approximately pH 8.0 for up to one hourbefore washing the gel slurry;

(e) washing the gel slurry first with an aqueous ammonium acetate orammonium bicarbonate solution, then with water to obtain a gelconductivity below 1,000 mmhos;

(f) acidifying and concentrating the gel slurry by adding acid to thegel slurry to achieve a pH below 6.0 while gradually removing water fromthe gel slurry; and

(g) drying and calcining the gel slurry to form the silica-aluminapowder material.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a mixer-reactor.

FIG. 2 is a top view of a mixer reactor.

FIG. 3 is a TEM Photomicrograph of Example Sample C1936-20-13 (EM 2829)taken at magnification 30 KX. It shows the particulate nature of thesample.

FIG. 4 is a TEM Photomicrograph of Example Sample EP-50 (EM 3309) takenat magnification 50 KX. It shows the gel network and small TiO₂particles.

FIG. 5 is a TEM Photomicrograph of Example Sample C1935-23B (EM 3821)taken at magnification 5 KX. It shows pockets and sheets.

FIG. 6 is a TEM Photomicrograph of Example Sample C1935-44B (EM 3735)taken at magnification 50 KX. It shows the pore size in the matrix.

FIG. 7 is a TEM Photomicrograph of Example Sample C1935-47B (EM 3728)taken at magnification 50 KX. It shows the pore size in the matrixgetting bigger than in FIG. 6.

FIG. 8 is a TEM Photomicrograph of Example Sample C1935-48B (EM 3743)taken at magnification 50 KX. It shows the pore size in the matrixgetting even bigger than in FIG. 7.

FIG. 9 is a TEM Photomicrograph of Example Sample C1252-36B (EM 0331)taken at magnification 10 KX. It shows the pore matrix without sheets.

FIG. 10 is a TEM Photomicrograph of Example Sample C1934-45 (EM 2269)taken at magnification 10 KX. It shows the dense matrix with manysheets.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to high surface area, amorphous silicaswhich form a continuous network matrix, rather than the typical smallparticles found in conventional amorphous silicas. Furthermore, the poresize and the distribution and volume of the pore size can be tailoredover a wide range so that the silicas have unique microstructures andvaried physical properties, such as surface area, pore volume, meanmesopore size, mesopore size distribution, macropore volume andacceptable fragmentation potentials and methods of making such silicas.

An especially significant aspect of the present invention is theachievement of “true” macropores in the amorphous silica material. Thesemacropores are “true” in the sense that their existence is verified andtheir structure observed and measured by TEM techniques, differing from“apparent” macropores which are observed and measured by mercuryporosimetry.

Mercury porosimetry is the common technique for measuring the amount ofmacropores in a catalyst sample. The technique involves subjecting thesample which was immersed in Hg to increasing pressure. The pressurechange starts from atmospheric (14 psi) to about 60,000 psi. The volumechange in the Hg level is monitored and plotted against the pressurechange. The change in Hg level was assumed to be the result of the Hgpenetrated into the pore spaces of the catalyst. The plot of the Hgvolume change against the applied pressure can then be presented as thepore size distribution of the catalyst.

However, when the skeletal framework structure of the catalyst departssignificantly from being infinitely rigid, some of the volume change inHg level recorded by the instrument comes about because the porouscatalyst particle was compressed or “squeezed” and not Hg penetratedinto the pores. Hence, the instrument could report the existence ofmacropores while in reality there were none present, especially in thecase of silica based catalysts. A detailed discussion of this phenomenonhas been published by Vittoratos and Auburn. (E. S. Vittoratos and P. R.Auburn, “Mercury Porosimetry Compacts SiO₂ Polymerization Catalysts”, J.of Catalysis, 152, 415-418 (1995)). TEM is the only technique to verifythe existence of true macropores. However, the usefulness of TEM toquantify the amount of macropores is at best quite limited, because ofthe difficulty of visually identifying and counting each macropore in aTEM micrograph.

It is thus clear that the mercury porosimetry instrument practicallyalways overestimates the amount of macropores. The true value matchesthe apparent (reported) value only for the limiting case of aninfinitely rigid sample. The apparent value can be positive even whenthe true value (verified by TEM) is zero. EP-50 is an example of acommercially available silica material which has been tested with themercury porosimetry method and apparent macropores were found but werenot verified by the TEM method.

The invention also relates to mixed silica-oxides in which the oxide isalumina, titania, zirconia, vanadia, etc., and combinations thereof,with unique microstructures, unique catalytic performance and variedphysical properties and methods of making such materials. Such mixedsilica-oxides also have continuous, tightly packed, gel network whichroutinely contain the unique sheet structures. Furthermore, the mixedoxides are homogeneous (i.e., no individual separate oxide phases areobserved), and the pore size, pore size distribution, and volume (meso)of these materials can be tailored also.

These silicas and mixed-oxide silicas are prepared via gelation ofsodium silicate alone or in combination with the precursors of the otheroxides. The gelation can proceed from either the acid or the base side,but it must be done with a high rate of mixing with shear forces. Thegel slurry can be washed at different pH's via a batch or via a V*Sepprocess to remove contaminant salts and to dewater the gel slurry. Thewashed gels may be aged at various pH's, temperatures and times to alterthe meso and macropore characteristics. Spray drying is the preferredmethod of forming and drying.

There are, of course, various types of mixing techniques and apparatuswhich generate varying levels of shear delivery mixing. See for example,“Scaleup and Design of Industrial Mixing Processes” by Gary B.Tatterson, McGraw-Hill, Inc. (1994) and especially FIG. 2.9 whichillustrates the shear level of various types of mixers and impellers.Referring to FIG. 2.9 of Tatterson, which is incorporated herein byreference, the colloid mills, saw blade type impellers; homogenizers andstator rotor mixers provide the highest level of shear while thehydrofoil and propeller provide the lowest shear. The newer jet streammixers can also be employed with sufficient shear as taught herein.

Shear in this specification means shear rate which is a change invelocity (ΔV) divided by a change in distance (Δd). For example, in arotor shear mixer, the fluids to be mixed usually are pumped into therotor stator chamber through concentric tubes. The rotor stator chamberconsists of a rotor revolving at some desired rate and a “stator” orsurrounding wall close to the tips of the revolving rotor. The wall isprovided with openings to permit the mixed fluids to be removed orwithdrawn quickly and continuously from the rotor-stator chamber.

Using the rotor stator mixer as an example, the velocity of the fluid ishighest at the tip of the rotor impeller and is zero at the wall. Thus,the ΔV is taken as the velocity at the tip which can be calculated bymultiplying the revolutions of the rotor per second times the radius ofthe rotor, i.e.:

 ΔV=ND/2

where N=revolution of the rotor per second; D=diameter of rotor.

The “change in distance”, Δd, is equivalent to the distance over whichone measures the change in velocity over the change in distance and iscalculated by the equation:${{Apparent}\quad {Average}\quad {Shear}\quad {Rate}} = \frac{\Pi \quad {ND}}{W}$

 Π=pi=3.1416

where

N is the revolutions of the impeller per second;

W is the distance between the tip of the impeller and the wall of themixer; and

D is the diameter of the rotor (in the case of rotor-stator mixer) orcan be the thickness of the impeller blade for other mixers.

It will be obvious to those with ordinary skill in the art that shearrates can be increased by increasing ΔV or decreasing Δd.

Gelling Silica Salts

It is possible to form gel from silica salts by either adding an acidsuch as sulfuric acid to sodium silicate or adding a base such asammonium hydroxide (sodium silicate plus acid). It is also possible toform gels from an acidic mixture of oxide precursors and a sodiumsilicate plus acid by adding a base such as ammonium hydroxide. In apreferred embodiment of making silica, adding acid to sodium silicatesolutions was used. The acid and base solutions were mixed withhigh-shear, continuous gelation (CHSG) using a two-stream feed systempumped directly into a Ross mixer (reactor). For gelling to occur in thehigh shear reactor, it was necessary to determine the acceptableconcentrations of the reacting silica salt, the pH, the temperature, themixing rate, and the stator configuration. Removing the residual saltsis important.

Achieving the right degree of washing with a batch (i.e., repulping andfiltering) or a continuous (i.e., V*Sep difiltration) process has asignificant effect on both the performance of the finished catalyst andthe outcome of any subsequent aging steps. The amount of residual saltinfluences the type and degree of aggregation of the primary particlessubsequently affecting the pore size and pore size distribution of thedried powder. In addition, an aging step definitely can be used to varyphysical properties of resultant SiO₂ bases.

Preparation of SiO₂ Powders

“General Procedure”

Step 1—Preparation of Solution of Silicate Anions

(A) Add the desired amount of sodium silicate to DI water with mixing.

(B) Dilute the sulfuric acid with DI water by weight.

Step 2—Relation

The silicate solution formed in Step 1 and sulfuric acid solution weresimultaneously pumped into the mixing chamber of a Ross-In-LineLaboratory Emulsifier (obtained from Charles Ross and Son Company,Hauppauge, N.Y., Model ME 300L) shown diagrammatically in FIG. 1(sideview) and FIG. 2 (topview). Referring to FIGS. 1 and 2, the basicsolution silicate anions prepared in Step 1A is pumped into the mixingchamber 10 through the outer ¼″ inside diameter tube 12 and the sulfuricacid prepared in Step 1B is pumped into mixing chamber 10 through theinner, ⅛″ inside diameter, tube 14. The mixing chamber 10 is fitted witha rotor impeller 16 having four arms and a stationary cylindrical wall18 surrounding the rotor impeller 16 and in relatively close proximityto the tips of the impeller arms. The stationary wall 18 is providedwith slots 20 through which the fluids and produced hydrogel pass intothe annular portions 22 of mixing chamber 10 and then out of the mixingchamber 10 through outer housing 24 and line 26. The acid and basesolutions react in the mixing chamber 10 while the rotor impeller 16operates at the desired revolutions per minute to provide the apparentaverage shear rate as taught above. The distance between the tip of onearm of impeller 16 and wall 18 is the “W” for use in the shear rateequation set forth earlier in this specification. The specific “W” forthe mixer-reactor used in the working examples below was 0.01 inches andthe diameter “D” of the rotor was 1.355 inches. The rate of addition ofthe acid and base solutions into the mixing chamber 10 is set to achievedesired pH at the outlet 24.

Step 3—Washing

The hydrogel was washed either by a batch process or by diafiltration.In one case, Examples 14 and 15, the same hydrogel was washed both ways.

Batch Washing

The hydrogel was blended with the desired wash solution in a Waringblender, mixed for about 15 minutes with a marine impellar mixer, andthen filtered. This was done until the conductivity of the filtrateequaled the conductivity of the wash solution. Then the hydrogel wasblended with DI water and filtered to yield a gel cake.

Diafiltration

The hydrogel in the holding tank was diluted with hot (50° C.) DI waterto about 4 to 10 weight percent solids as measured by an LOM instrument(CEM AVC 80).

This dilute hydrogel was washed on a vibrating filtration membranemachine (New Logic International V*SEP machine (Series P) where V*SEPstands for Vibratory Shear Enhanced Processing). This washing processknown as difiltration involves dewatering the hydrogel and adding freshDI water at the same rate at which the filtrate or permeate containingthe contaminated salts is removed. The washing is continued until thedesired conductivity of the permeate as measured by a conductivity meter(Yokogama Model SC400 conductivity converter) is achieved.

Once the desired conductivity was achieved, the hydrogel solution wasconcentrated to the maximum “pumpable” weight percent solids (by LOM).

This was done by dewatering the hydrogel solution by not adding fresh DIwater.

Step 4—Aging

The washed hydrogel was filtered to yield a filter cake. The filter cakewas diluted with DI water to allow for mixing with a marine impellarmixer. The pH of the slurry was adjusted with either acetic acid to a pHequal to about 5.6 or with ammonium hydroxide to a pH equal to about9.6. The pH adjusted slurry was heated to 50° C. over about 15 minutesand then held at 50° C. for about 15 minutes. The hot aged slurry wasthen pumped to the feed system of the spray dryer.

Step 5—Drying

Vacuum Drying

The gel cake was dried in a vacuum oven at 80° C. overnight.

Spray Drying

The hydrogel from Step 3 or 4 was pumped to the feed system of a StorkBowen BE 1235 spray dryer and dried. The spray dryer conditions werevaried, by means well known to those having ordinary skill in the art,to achieve a desired particle size, LOM moisture weight percent andother desired characteristics.

Step 6—Calcination

The spray dried from Step 5 was calcined in a muffle furnace for onehour at 400° C.

The vacuum dried hydrogel was calcined in a muffle furnace for one hourat 400° C.

In some Examples below, the uncalcined (as vacuum dried or spray dried)silica was impregnated with a chromium salt to deposit about 1 weightpercent chromium on the support on an LOI basis, done at 1000° F. forone hour. Chromium impregnation is done using a Buchi rotovap. A maximumof 50 g of powder is added to a 500 ml rotovap flask. About 75 to 100 gof the solvent methanol or DI water is added to the powder (solvent topowder ratio is always approximately 2 to 1 by weight). Swirl the flaskto achieve uniform wetting of the powder. Weigh the chromium (III)acetate hydroxide and dissolve in the solvent (approximately 15-30 ml).Add the chromium solution to the powder slurry and swirl to evenly coatthe powder. Attach flask to the Buchi and spin the flask forapproximately 5 minutes without vacuum to mix the slurry. Using a vacuumregulator and vacuum pump, set the vacuum to approximately 200 to 400 mmHg, and lower the flask into an 80° C. water bath when water is thesolvent or a 40° C. water bath when methanol was the solvent. Maintainthese conditions until approximately 80% of the solvent was evaporated.Slowly increase the vacuum to approximately 600 mm Hg as necessary toremove the last of the solvent without “bumping” any of theslurry/powder over. When the powder appears completely dry, increase thevacuum to maximum for approximately 5 minutes. After the last vacuumadjustment is complete, release the vacuum and shut off the Buchi.

Such silicas and mixed silica-oxides have a wide variety of uses,especially as supports for ethylene polymerization. Also, because of thecatalytic and physical properties, the mixed silica-oxides can betailored for use as FCC catalysts or for use in hydroprocessing such ashydrodenitrification, hydrodesulfurization, hydrodewaxing, hydrocrackingor hydrogenation.

The physical properties such as surface area and pore size and pore sizedistribution can differ significantly not only between hydrogels andprecipitates of silicas and mixed oxide silicas, but even betweenvarious types of precipitates depending on the treatment of theprecipitates both during and after preparation, i.e., hot washing; hotaging, etc.

Certain silica and mixed oxide silica precipitates have now beendiscovered which have excellent thermal and physical stability, togetherwith a relatively high amount of macroporosity so that these materialsare particularly suited for use as catalyst support materials,especially for use in reactions involving relatively large molecules(e.g., residua) in order to allow the molecules easy ingress and egress.

The silica and mixed oxide silicas are characterized by being amorphous;having a non-particulate, dense, continuous network matrix, and havingencapsulated regions with true macropores. Some of the silica and thesilica-alumina precipitates have also been found to have sheet-likemicrostructures.

The new silicas and mixed oxide silicas have, in addition, certaincharacteristics in their preferred form as set forth below. Thesecharacteristics were determined after drying and calcining the silicasat 400° C. for 1 hour and mixed oxide silicas, i.e., silica-aluminas, at593° C. for 2 hours.

(1) Surface area by the BET Method

Typically, the surface area of the new silicas and mixed oxide silicasis from about 150 to 600 m²/gm.

(2) Macropore Volume by the Mercury Technique

By “macropore volume” in this specification is meant the volume occupiedby pore sizes in excess of 1000 Å. It is particularly desirable for someend uses such as the polymerization of olefins to have a macroporevolume in excess of 0.1 cc's per gram. The problem in the past wasobtaining supports with a “true” macropore volume in excess of 0.1 cc'sper gram along with physical stability. The silicas and mixed oxidesilicas of this invention have a high macropore volume and arephysically stable as shown by the fact they were successfully used in afluid bed gas phase polymerization of ethylene.

The macropore volume is taken by the mercury porosimetry test (by ASTMDesignation: D4284-88 where gamma is taken to be 473 dynes per cm andthe contact angle is taken to be 140 degrees).

The macropore volumes of the new silicas and mixed oxide silicas are atmost 0.5 cc's per gram.

(3) Mean Mesopore Diameter by the BET Method

The mean mesopore diameter of the silicas and mixed oxide silicas can befrom 60 to about 250 Å.

(4) Fragmentation Potential and Sonication Number

The testing of catalysts so as to determine attrition characteristics isrecognized in the art. These tests typically involve introduction ofcatalyst particles into a vessel and subsequent agitation of theparticles. In such an arrangement, attrition results primarily fromabrasion caused by particles impacting with each other as well as withthe wall of the vessel.

For example, in processes where particles are subjected to fluidized bedconditions, fluidized tests such as air-jet testing are common in as faras they can be considered directly relevant to the performance ofparticles under such conditions.

While such tests can be effective in testing attrition under certainconditions, they have largely proven ineffective with respect topredicting the effectiveness of catalysts in processes where theattrition is related to the fractionation of the catalyst.

Moreover, such techniques fail to accurately report that polymerizationcatalysts, unlike catalysts employed in other processes,. e.g.,catalytic cracking, are subject to attrition at two different stages,i.e., activation and polymerization. Thus, while traditional techniques,e.g., air-jet testing, may provide an effective model for attritionoccurring during activation, such techniques are not an effective modelfor attrition occurring during polymerization and thus are notsufficient to deal with such catalysts.

One particular process in which fractionation of the catalyst occurs isthe polymerization of olefins. Olefin polymerization processes are wellrecognized in the art. Typical examples of such processes include slurrybatch, e.g., slurry loop and gas phase olefin polymerization processes.

Although each of these processes utilize catalysts in the production ofpolyolefins such as polyethylene, they differ significantly with respectto the dynamics of particle growth therein. For example, gas phaseprocesses include as much as 85% ethylene while slurry loop typeprocesses have a much lower ethylene solubility, e.g., typically 8%maximum. Accordingly, catalysts which may be effective in one olefinpolymerization process may not be found effective in another process.The new silica supported polymer catalysts of this invention areeffective in batch polymerization processes. One aspect of the presentinvention is based upon the surprising discovery that the “fragmentationpotential” of catalysts, such as olefin polymerization catalysts, asdetermined by sonication, can be used in determining the expectedefficiency of a catalyst in a process where fragmentation will occur.

The sonication process for use in the present invention can effectivelybe employed within any sonication environment with sonication baths, andin particular sonication baths employing water, being preferred.

This sonication test can then typically take on one of two forms. Thematerial can be sonicated for a predetermined period of time, e.g., 30minutes, and the increase in fines, e.g., percent increase, subsequentto sonication can be determined. This test directly provides what iscalled the “fragmentation potential”.

Alternatively, the material can be sonicated for a period of timesufficient to reach a preselected mean particle size. The result of thisparticular test is called the “Sonication Number”. Although thisspecification will typically make reference to the fragmentationpotential, the concepts and advantages are the same for both of thesebasic tests.

In fact, as is readily apparent, these tests are basically analogouswith the numerical results being inversely related. That is, a catalystwhich has a small increase in fine production over a predeterminedperiod of time will typically require a longer time to reach thepreselected mean particle size. The inverse is also true; a catalysthaving large percent increase in fine production will have a smallerrelative period of time to reach the predetermined mean particle size.

The particular sonication test employed is not critical to the presentinvention and the selection of test and equipment is largely determinedby practical considerations such as time allotted to perform the test.

For purposes of this specification, the “fragmentation potential” isdefined as the percent increase in the percentage of particles which aresmaller than 40 microns after sonication for 30 minutes in the aqueousmedium, plus a dispersant using an Horiba LA 900 instrument. Calculationof the fragmentation potential, of course, involves taking the percentof particles which are smaller than 40 microns after 30 minutes andsubtracting the percent of particles smaller than 40 microns in thesample before sonication. It was recognized that the initial samplecould have some spheres of less than 40 microns agglomerated withsomewhat larger spheres. A preferred variation is to initiallydegglomerate the sample by sonicating the sample for one minute toobtain a base value for the percent of particles smaller than 40 micronsbefore sonicating for 30 minutes as described herein. In this instance,the fragmentation potential is calculated by taking the percent ofparticles smaller than 40 microns after 30 minutes and subtracting thepercent of particles smaller than 40 microns in the sample after aninitial one-minute sonication. The fragmentation potential using thepreferred technique is lower, as expected. In the data to be givenbelow, the fragmentation potential is given as (30-0) or (30-1), the “0”indicating no pre-sonication, and the “1” indicating a pre-sonication ofone minute. In an analogous test, the sonication number is determined asthe time for the mean particle size of a test sample to fall to 40microns.

Preferably, the fragmentation potential is from 10 to 84 percent, morepreferably above 30 percent, and most preferably above 30 to 60 percent.

Similarly, the Sonication Number is preferably from 5 to 200 minutes,more preferably from 10 to 150 minutes, and most preferably from 20 to100 minutes. These numbers are obtained when using a Molvern ParticleSize Analyzer with a 300 mm focal length and an active beam length of 2mm.

The fragmentation potential and sonication numbers set forth above arefor the silicas and mixed oxide silicas of this invention aftercalcining at 400° C. for 1 hour. The fragmentation potential andsonication number will, of course, vary depending on whether thecatalyst base is tested before or after calcining; before or after theaddition of chromia, etc. Likewise, the optimal fragmentation potentialwill differ from other bases such as silica.

While not wishing to be bound by any theory, it is believed thesonication technique is a unique tool for providing a fingerprint of animproved ethylene polymerization catalyst because of the shattering ofthe particles as shockwaves move through the internal pore structure.Accordingly, it is believed that such a process closely resembles thefracturing process which can occur during polymerization, i.e., thecatalyst particle breakup due to the accumulation of polymer andpressure within the pore structure.

(5) Microscopy

The new silica and mixed oxide silica compositions of this inventionpossess very unique and important characteristics over the silicas andmixed oxide silicas of the prior art, i.e., the new silicas and mixedoxide silicas have a microstructure of encapsulated regions with truemacropores within a non-particulate, dense, continuous network matrix.And in one embodiment, they also exhibit sheet structures.

Physically, the new silicas and mixed oxide silicas are spray dried toform a non-particulate, dense, continuous network matrix withencapsulated regions of true macropores. The mean mesopore diameter isin a range of from 60 to 250 Å. The microscopic examination of theseregions is done using standard transmission electron microscope (TEM)techniques. For example, to observe the TEM specimen in the bright fieldimaging mode, it is necessary to prepare the TEM specimen by themicrotomy technique.

The microtomy technique is a well established specimen preparationtechnique in the field of transmission electron microscopy. Itsdescription can be found in standard reference published literature, forexample, T. F. Malis and D. Steele, “Ultramicrotomy for MaterialsScience”, in “Workshop on specimen preparation for TEM of materials II”,ed. R. Anderson, vol. 199, Materials Research Symposium Proceedings(MRS<Pittsburgh, 1990) and N. Reid, “Ultramicrotomy”, in the “Practicalmethods in electron microscopy” series, (ed. A. M. Glauert, publ.Elsevier/North Holland, 1975). Briefly, it involves embedding the samplein a resin, form a pellet by polymerizing the resin in a mold, then cutthin sections using a microtome equipped with a diamond knife. In thework for this specification, the resin used was L. R. White resin. Thetypical thin section would have a thickness of about 0.06 microns. Careneeds to be taken to embed whole encapsulated regions in order thatviews of the entire random cross sections of the true macropores arepresented. Furthermore, it is important that prudent sampling techniquesbe used to collect the sample to be used for the TEM specimenpreparation step. The portion of encapsulated regions that were embeddedshould be selected from a sample by sequentially dividing the originallycollected sample into quarter portions until the desired amount ofmaterial suitable for the embedding process is reached.

In the TEM examination of specimens, it is always a balance between theamount of details to be observed and the amount of material to beexamined to ensure representativeness. To observe the increasing detailsof relevant microscopic features requires higher magnifications whilethis decreases the filed of view and the amount of material examined.However, a modern microscope allows the operator to easily changemagnifications from 100× to 1,000,000×. It is standard practice tosurvey the sample at low magnifications, identify and confirm the viewsthat are typical and representative of the sample, then increase themagnification as necessary to examine the details. Images will then berecorded to illustrate the characteristics of the sample. The recordedimages (which usually are on a 3.25″×4″ negative) are then printed andusually further magnified.

Such further magnification occurs by printing, for example, to an8.5×11″ print.

For the purposes of this specification, the images of photomicrographshave destination magnifications between 3000× and 150,000×. The term“destination magnification” refers to the final magnification of theprinted image.

EXAMPLES

The invention will be further illustrated by the following examples,which set forth particularly advantageous method embodiments. While theExamples are provided to illustrate the present invention, they are notintended to limit it. The following are non-limiting examples ofexperiments involving the making and testing of both silicas and mixedsilica oxides.

Tables 1 and 1A summarize the key process variables and the resultingphysical properties of the formed and calcined SiO₂ powder resultingfrom the CHSG experiments. Examples 1 through 13 SiO₂ powders wereformed by vacuum drying the gel-cake, and crushing and sizing. Examples14 through 17 were spray dried with the Stork Bowen spray-dryer.

Both sets of samples were calcined at 400° C. for one hour prior tocharacterization.

Tables 2 and 3 summarize the observations associated with each of theCHSG, continuous, high shear, experiments.

TABLE 1 Summary of the Preparation Conditions for the SiO₂-bases of ThisInvention Example No 1 2 3 4 5 6 7 8 Notebook No C1935-23A C1935-23BC1935-23N C1935-31 C1935-38A C1935-38A C1935-38B C1935-38B(3) I)Solutions Na₂O:SiO₂, 1:3.22, Kg 0.6831 0.6831 0.6831 1.591 1.75 1.751.75 1.75 (Banco Sodium silicate 41 Be DI H₂O, Kg. 2.5 2.5 2.5 7 7 7 7 7pH 11.8 11.8 11.8 12.2 12.2 12.2 12.2 12.2 w/w DI H₂O/H₂SO₄ 3 to 1 3 to1 3 to 1 6 to 1 6 to 1 6 to 1 6 to 1 6 to 1 pH 1.1 1.1 1.1 1.01 1.2 1.21.2 1.2 II) Gelation Stator configuration Slot Slot Slot Slot ScreenScreen Screen Screen RPM of Rotor 7563 7563 7563 7723 7700 7700 77007700 Apparent Average Shear 5.36 5.36 5.36 5.48 5.46 5.46 5.46 5.46 Rate× (10)⁴ pH Range 2 to 10 2 to 10 2 to 10 5 to 7 5 to 7 5 to 7 5 to 7 5to 7 Acid Rate, gm/min 72 to 220 72 to 220 72 to 220 100 67 67 67 67Base Rate, gm/min 630 to 670  630 to 670  630 to 670 548 351 351 351 351pH at outlet — — — 7.5 9 9 9 9 Gel T, C. 21 21 21 21 20 20 20 20 III)Washing Batch Yes Yes Yes Yes Yes Yes Yes Yes Wash Solution NH₄ NH₄ NH₄NH₄ NH₄ NH₄ NH₄ NH₄ Acetate Bicarbonate Nitrate Acetate Acetate AcetateBicarbonate Bicarbonate pH of Wash Solution 7.3 8.4 5.3 7.3 7.3 7.3 8.48.4 Wash Temperature, C. Ambient Ambient Ambient 50 Ambient 50 Ambient50 Conductivity of Water Wash (1) Initial, mmhos/cm² 8400 — 9250 80007000 10000 6800 7250 (2) Final 2300 1200 2600 2400 1950 2600 1350 500Water Wash Temperature, C. Ambient Ambient Ambient 50 Ambient 50 Ambient50 Diafiltration No No No No No No No No Dilution, Wt % Solids (LOM)Wash Solution pH of Wash Solution Conductivity of Water Wash (1) Initial(2) Final Water Wash Temperature, ° C. Wt % Solids of Concentrate IV)Aging pH Acid/Base Time, Min. Temperature V) Drying 80° C. in 80° C. in80° C. in 80° C. in 80° C. in 80° C. in 80° C. in 80° C. in VacuumVacuum Vacuum Vacuum Vacuum Vacuum Vacuum Vacuum VI) Physical Properties(2) Surface Area (BET), m²/gm 177 476 468 503 501 464 426 445 PoreVolume (BET) cc/gm 0.521 0.939 0.924 1.004 0.929 0.998 0.949 0.985 MMPD,A 128 100 96 81 96 115 117 119 Particle size, microns AASR = ApparentAverage Shear Rate, reciprocal seconds (2) Measurement made aftercalcination for 1 hr at 400° C.

TABLE 1A Summary of the Preparation Conditions for the SiO₂-Bases ofThis Invention Example No 9 10 11 12 13 14 15 16 17 Notebook No C1935-43C1935-42 C1936-50A C1936-50B C1936-50N C1935-44B C1935-44B C1935-47C1935-48 I) Solutions Na₂O:SiO₂, 1:3.22, Kg 1.75 1.75 0.683 0.683 0.6834.098 4.098 4.098 (Banco Sodium silicate 41 Be DI H₂O, Kg. 7 7 5 5 5 1515 15 pH 12.2 11 11 11 11 11.2 11.2 11.2 w/w DI H₂O/H₂SO₄ 6 to 1 6 to 13 to 1 3 to 1 3 to 1 6 to 1 6 to 1 6 to 1 pH 1.2 <0 1.3 1.3 1.3 <0 <0 <0II) Gelation Stator configuration Screen Screen Screen Screen ScreenSlot Slot Slot RPM of Rotor 7700 7800 2729 2729 2729 10200 9923 9923Apparent Average Shear 5.46 5.53 1.93 1.93 1.93 7.23 7.04 7.04 Rate ×(10)⁴ pH Range 5 to 7 6.9 to 8.5 5 to 7 5 to 7 5 to 7 2.3 to 4.8 5.5 5.5Acid Rate, gm/min 67 145 50 50 50 127 150 150 Base Rate, gm/min 351 692680 680 680 450 to 639 650 650 pH at outlet 9 7.3 — — — 6.5 4.1 4.1 GelT, ° C. 20 23 24 24 24 30 28 28 III) Washing Batch Yes Yes Yes Yes YesNo Yes No No Wash Solution NH₄ Bi- NH₄ Bi- NH₄ NH₄ NH₄ NH₄ carbonatecarbonate Acetate Bicarbonate Nitrate Bicarbonate pH of Wash Solution8.4 8.4 7.3 8.4 5.3 7.9 Wash Temperature, C. 50 50 Ambient AmbientAmbient 50 Conductivity of Water Wash (1) Initial, mmhos/cm² 7250 7250 —— — 6700 (2) Final 500 500 2300 1400 1400 1233 Water Wash Temperature,C. 50 50 Ambient Ambient Ambient 50 Diafiltration No No No No No Yes YesYes Dilution, Wt % Solids (LOM) 2 3 3 Wash Solution NH₄ Bi- NH₄ Bi- NH₄Bi- carbonate carbonate carbonate pH of Wash Solution 7.9 8 8Conductivity of Water Wash (1) Initial 9360 — — (2) Final 300 2000 2000Water Wash Temperature, 50 50 50 ° C. Wt % Solids of Concentrate 9 8.848.84 IV) Aging Yes No No Yes Yes pH 5.1 5.6 9.6 Acid/Base Acetic AceticNH₄ acid acid Hydroxide Time, Min. 10 30 30 Temperature 38 50 50 V)Drying 80° C. in 80° C. in 80° C. in 80° C.in 80° C. in Spray Dry 80° C.in Spray Dry Spray Dry Vacuum Vacuum Vacuum Vacuum Vacuum Vacuum VI)Physical Properties (2) Surface Area (BET), m²/gm 417 476 570 475 515538 to 561 378 471 to 487 454 to 474 Pore Volume (BET) cc/gm 1.128 0.8440.815 0.842 0.787 1.02 to 1.3 0.956 1.1 to 1.2 1.3 to 1.4 MMPD, A 162 7967 82 71 101 to 140 114 140 to 167 151 to 167 Particle size, microns 6349 60 AASR = Apparent Average Shear Rate, reciprocal seconds (2)Measurement made after calcination for hr at 400° C.

TABLE 2 Comparison of the Physical Properties and the Microstructure ofthis Invention to Other Sources of SiO_(2 Bases) SiO₂- CommercialCommercial Source of SiO₂ Dispersion SiO₂ SiO₂ CHSG-Invention ExampleComparative Comparative Comparative 1 2 5 14 16 17 Sample ID C1936-20-13EP-30x EP-50 C1935-23A C1935-23B C1935-38A C1935-44B C1935-47B C1935-48BSurface Area (BET) 166 309 451 177 476 501 564 487 474 Pore Volume, PV,0.417 1.63 2.096 0.523 0.94 0.929 1.02 1.21 1.318 (N₂) Mean Meso Pore113 206 183 128 100 96 101 140 151 Diameter, Å Geometric Pore 88 — 161104 72 66 64 88 97 Diameter, Å Pore volume 0.2505 — 2.06 0.423 0.2640.2199 0.2387 0.7187 0.88 (N₂) > 100A Pore volume 0.0082 — 0.395 0.00790.0319 0.04 0.0729 0.1554 0.188 (N₂) > 200A Pore volume 0.0029 — 0.01570.0021 0.0083 0.0083 0.0133 0.0275 0.037 (N₂) > 500A Fragmentation — —′39 — — — 28 22 22 Potential (30-1 min) “Apparent” Macro Yes Yes Yes — —— Yes Yes Yes PV (Hg) > 1000A Macro PV (Hg), 0.529 0.15 0.492 — — —0.215 0.38 0.44 cc/gm “True” Macro PV No ? No Yes Yes Yes Yes Yes Yes(TEM) Microstructures (TEM) Particulates x x Continuous network x x x xx x x matrix Pockets (Lower x x x x x x density than matrix) Sheets x x

TABLE 3 TEM Characterization of SiO₂ Bases of the Prior Art and of thisInvention SiO₂- Commercial Commercial Source of SiO₂ Dispersion SiO₂SiO₂ CHSG-Invention Example Comparative Comparative Comparative 1 2 5 1416 17 Sample ID C1936-20-13 EP-30x EP-50(SiO₂/TiO₂) C1935-23A C1935-23BC1935-38A C1935-44B C1935-47B C1935-48B Particulates x x None None NoneNone None None Size of Partic- 17 N. A. ulates, nm Size of Pores 10(estimated) Continuos x x x x x x x network matrix Density of 3⁺ 1 3 2 24 Matrix Size of Matrix 20    8 7 10  10  25  Pores, nm Pockets x x x xx x Density of 5 1 3 2 2 Pockets Size of Pockets 1 2 3 3 3 Size ofPockets ˜15 Microns ˜10 Microns <10 Microns <10 Microns <10 MicronsPorosity of 3 1 3 2 2 Pockets Size of Pocket 70  85  20  30  80  Pores,Typical, nm Size of Pocket 30 to 120 24 to 250 10 to 24 20 to 200 25 to200 Pores, Range, nm Sheets x x Quantity of Only Only sheetsoccasionally occasionally observed observed Size of sheets About 0.02-About 0.1 0.15 microns microns thick and thick and 5- several 10 micronsmicrons length long

The General Procedure set forth above using the high shear mixer wasemployed with specific amounts of reactants; shear rate, etc. as setforth in Tables 1 and 1A above. The characteristics of the silica aresummarized in Tables 1, 1A and 2.

Referring to Table 2, the silica possessed “true” macropore volume asobserved by TEM. It also possessed a continuous network matrix, withpockets of less density and occasional “unique” sheet microstructures.

Table 3 summarizes the characteristics of the matrix, pockets and sheetsas observed by TEM.

Examples 1-2-3

Example 1 was split in thirds. Example 2 was washed initially with anammonium bicarbonate solution as noted in Tables 1 and 1A. Example 3 waswashed initially with an ammonium nitrate solution as noted in Tables 1and 1A. Both were then washed with DI water.

Referring to Tables 1 and 1A, Examples 2 and 3 had higher surface areasthan Example 1; they had higher pore volumes; they had lower mean mesopore diameters. This shows that washing affects the physical propertiesof the silica.

Referring to Table 2, Example 2 possessed “true” macropore volume asobserved by TEM. It also possessed a continuous network matrix withpockets of less density and occasional “unique” sheet microstructure.The “true” macropore volume of Example 2 was less than that of Example1.

Table 3 summarizes the characteristics of the matrix, pockets and thesheets observed the TEM of Example 2. TEM showed that the density of thematrix of Example 2 was less than that of Example 1. However, thedensity of the pockets was higher. Example 2 had smaller pockets whichcontained smaller pores.

Chromium (III) acetate hydroxide was deposited onto the silica to resultin 0.7 weight percent chromium. The silica was first calcined at 400° C.for 1 hour. The chromium compound was dissolved in methanol.

Example 4

Example 1 was repeated except for the differences noted in Tables 1 and1A.

Examples 5-8

Example 1 was repeated using a screen stator and the differences notedin Tables 1 and 1A. All the silica powders were high surface area, 428to 501 m²/gm. These examples illustrate the effects the washingsolution, washing conditions and degree of washing have on the physicalproperties.

Referring to Table 2, Example 5 possessed a continuous network matrix,pockets, but no sheets. It also possessed “true” macropore volume.

Table 3 summarizes the characteristics of the matrix and the pocketsobserved in the TEM of Example 5. Example 5 had the least dense matrix,compared to Examples 1 and 2. Example 5 had the most porous pockets withpores ranging from 24 to 250 nm (240 to 2500 Å).

Example 9

Example 5, 20 grams, was blended with 400 grams of Di water and aceticacid in a Waring Blender. The pH was about 5.1. The mixture was blendedfor about 12 minutes. The final temperature was 38° C. The blend wasfiltered. The gel-cake was vacuum dried at 80° C. overnight. It was thencalcined at 400° C. for one hour and then ground and sized. Compared toExample 5, Example 9 had a lower surface area, 417 m² /gm versus 501m²/gm. But Example 9 had both a larger pore volume, 1.128 cc/gm versus0.929 cc/gm, and a bigger MMPD, 182 Å versus 96 Å.

Example 10

Example 10 was essentially a repeat of Example 8 except for thedifferences noted in Tables 1 and 1A.

Examples 11-13

The General Procedure set forth above using the high shear mixer wasemployed with the specific amounts of reactants; shear rate, etc., asset forth in Tables 1 and 1A above. These silicas were prepared at a lowAASR employing the screen stator.

Referring to Tables 1 and 1A, which summarizes silica characteristics,all these silicas were high surface area, greater than 470 m²/gm.

Examples 14, 16 and 17 were washed by difiltration and formed by spraydrying.

Example 14

The General Procedure set forth above using the high shear mixer wasemployed with the specific amounts of reactants, shear rate, etc., asset forth in Tables 1 and 1A above.

Referring to Tables 1 and 1A, this silica powder had higher surfacearea, more pore volume, and a larger MMPD than the previous examples,illustrating the impact of washing by difiltration and forming by spraydrying.

Referring to Table 2, the silica powder possessed macropore volume asmeasured by mercury porosimetry, about 0.215 cc/gm. It also possessed“true” macropore volume as observed by TEM. It was comprised of acontinuous network matrix and pockets of less dense material. Thefragmentation potential of this powder was 28.

Table 3 summarizes the characteristics of the matrix and pockets asobserved by TEM.

Chromium (III) acetate hydroxide dissolved in methanol was depositedonto the silica powder to result in 1.0 weight percent chromiumcatalyst. Chromium (III) acetate hydroxide dissolved in DI water alsowas deposited onto Example 14 to result in a second 1.0 weight percentchromium catalyst.

Example 15

A portion of Example 14 was batch washed as set forth above in theGeneral Procedure, and formed after vacuum drying by grinding thegel-cake as set forth in Tables 1 and 1A above.

Referring to Tables 1 and 1A, this silica powder, compared to Example14, had a lower surface area, 378 m²/gm versus ˜550 m²/gm, a lower porevolume, 0.958 cc/gm versus about 1.2 cc/gm, and smaller MMPD.

Example 16

Example 14 was repeated using the differences noted in Tables 1 and 1Aabove. Acetic acid was added to the gel and enough DI water to allow formixing with a Marine impeller mixer. (The pH of the slurry adjusted to5.6.) The mixture was heated to 50° C. over 15 minutes and held at thattemperature for about 15 minutes. The slurry was spray dried.

The characteristics of the silica powder are summarized in Tables 1, 1A,and 2.

Referring to Table 2, Example 16, compared to Example 14, had a lowersurface area, 487 m²/gm compared to 564 m²lgm, but the pore volume waslarger, 1.21 cc/gm versus 1.02 cc/gm, and the MMPD was bigger, 140 Åversus 101 Å. The “apparent” macropore volume was also larger, 0.38cc/gm compared to 0.215 cc/gm. Example 16 had “true” macropore volume asobserved by TEM. This clearly illustrates the benefit of hot aging inacid conditions. The fragmentation potential of this powder was 22.

Table 3 summarizes the characteristics of the matrix and the pockets.The hot aging in acid pH changed the characteristics of the pockets.Compared to Example 14, Example 16, after aging as described above, hadmore porous pockets with larger typical pores, 300 Å versus 200 Å, and awider range of pores in the pockets, 200 Å to 2000 Å versus 100 Å to 300Å.

Example 17

Example 14 was repeated using the differences noted in Tables 1 and 1Aabove. Ammonium hydroxide was added to the material of the gel andenough DI water to allow for mixing with a marine impeller mixer. The pHwas adjusted to about 9.6. The mixture was heated to 50° C. over 15minutes and held at 50° C. for 15 minutes. The slurry was spray dried.

The characteristics of the silica powder are summarized in Tables 1, 1A,and 2.

Referring to Table 2, Example 17 compared to Example 14, had a lowersurface area, 474 m²/gm to 564 m²/gm, but the pore volume was larger,1.318 cc/gm versus 1.02 cc/gm, and the MMPD was bigger, 151 Å versus 101Å. The “apparent” macropore volume was also larger, 0.44 cc/gm versus0.215 cc/gm. Example 17 had “true” macropore volume as observed by TEM.This clearly illustrates the benefit of hot aging in base conditions.The fragmentation potential of this powder was 22.

Table 3 summarizes the characteristics of the matrix and the pockets.The hot aging in base pH changed the characteristics of both the matrixand the pockets. The density of the matrix decreased and the size of thematrix pores increased to 250 Å compared to 100 Å for Example 14.Compared to Example 14, Example 17, after aging as described above, hadmore porous pockets with larger typical pores 800 Å versus 200 Å, and awider range of pores in the pockets, 250 to 2000 Å versus 100 to 300 Å.

Chromium (III) acetate hydroxide dissolved in methanol was depositedonto Example 17 to result in 1.0 weight percent chromium.

Silicas of this invention, such as Examples 1, 2, 7 and 14, made viagelation of sodium silicate (base side) by sulfuric acid under shearconditions contain the microstructures described above. This is incontrast to a commercial silica base used for ethylene polymerizationdescribed in Example 19 which contain neither the sheets nor theencapsulated, non particulate regions with true macropores.

This is also in contrast to experimental materials made from commercialdispersions and blends of those dispersions.

Comparative Example 18 Gelling Commercially Available SiO₂ Dispersions

Two dispersions and mixtures thereof were used, with the SiO₂ in eachdispersion having a different microstructure. They were (1) Nyacolcolloidal silica, 40 Wt. % SiO₂ (amorphous) with a spherical structure;and (2) Snowtex-UP, 20-21 Wt. % SiO₂ (amorphous) with a fiber structure.In order to achieve the gelling of each dispersion, it was necessary todetermine the acceptable concentrations of the reacting SiO₂s, the pH,the temperature, and the type of mixing to achieve gelation in areasonable time. This was accomplished by using a heated glass reactorfitted with a marine-impeller mixer or polytron mixer and a means togradually adjust the pH of the reaction. Because the dispersionscontained minimal amounts of residual salts, washing the resulting gelwas not necessary.

Comparative Table 4 summarizes the key process variables and theresulting microstructure of the formed and calcined SiO₂ powdersresulting from the experiments done with the commercial SiO₂dispersions. All the gel slurries were formed by spray drying with theYamato spray dryer, Model DL-41 and the resulting powders were calcinedin a muffle furnace at 400° C. for one hour. The experimental SiO₂'s(comparative examples) made from commercially available dispersions areas follows:

(1) 1936-21-32, made from 100 Wt. % Snowtex (fibers);

(2) 1936-45, made from a 50/50 blend of Snowtex (fibers) and Nyacol(spheres);

(3) 1936-20-13, made from 100 Wt. % Nyacol (spheres).

COMPARATIVE TABLE 4 Sample 1936-21-32 1936-45 1936-20-13 Gel pH 4.93 5.65.13 Temp. ° C. 58 50 38 Gel time Overnight 6 min 39 min Mixer PolytronMarine impellar Polytron Blend 100% 50% Snowtex/50% Nyacol 100% NyacolSnowtex Particulate <100 Å >100 Å ˜170 Å size: MMPD, Å 144 78 113Packing: Densely Densely packed with large Densely packed packed cracksin about ⅓ of the with uniformly larger formed particles formed spheres

Comparative Example 19 Physical and Microstructural Characteristics ofthe Silicas of this Invention Compared to Commercially Available Silicasand Silicas Made from Silica Sols

SiO₂ powders of Comparative Table 4 were characterized. Thecharacterization can be broken down into three categories: commercialSiO₂ (commercial dispersions and blends), and experimental SiO₂(commercial dispersions and blends), and experimental SiO₂ (silicasalt/CHSG). The commercial materials are EP 30x and EP-50. Theexperimental SiO₂'s (comparative examples) made from commerciallyavailable dispersions are as follows:

(1) 1936-21-32, made from 100 Wt. % Snowtex (fibers);

(2) 1936-45, made from a 50/50 blend of Snowtex (fibers) and Nyacol(spheres);

(3) 1935-11, made from a 25/75 blend of Snowtex (fibers) and Nyacol(spheres); and

(4) 1936-20-13, made from 100 Wt. % Nyacol (spheres).

The experimental SiO₂'s made by gelling sodium silicate with acid viaCHSG are 1, 2, 5, 14, 16 and 17. The TEM data for several of these basesis summarized below.

The matrix of EP-30x was mostly made up of individual particles ofirregular shapes and sizes. There were some areas where the particlesappeared to be sintered together and resembled the appearance of thecontinuous network. These areas were only a small fraction of the totalvolume of the sample.

EP-50 was made up of a continuous porous network of amorphous SiO₂. Thepores appear to be about 200 Å. This is consistent with the valueobtained via BET, about 183 Å. EP-50 contains TiO₂. The TEM analysissuggests that the TiO₂ is present as a second phase in the form of fineparticles of about 10 Å and less in size.

The SiO₂ bases made from the dispersions and spray dried via the Yamatoappeared as smooth rounded macroscopic particles of uniform density. Thelarger spray dried particles, 5-20 microns, are made up of smaller,densely packed individual particles.

The different microstructures of the starting dispersions affect thesize of the particulates present in the microstructure. In fact, itlooks like the ratio of the fibers to spheres affects size and thepacking of the particulates in the microstructure: the amount ofcracking in the spray dried particles increases with the amount offibers, Snowtex, present in the blend.

The spray-dried SiO₂'s made from CHSG exhibit different microstructuresfrom the preceding materials. They consist primarily of anon-particulate, dense, continuous-network matrix and not individual,fundamental particles. The secondary structure is composed of pockets ofless density, non-particulate regions with true macropores. The size ofthese pockets, ranging from 2 μm to 15 μm, varies with the preparationconditions. The density of the non-particulate, dense,continuous-network matrix also varies with the preparation conditions.Examples 1, 2, 5 and 14 (V*SEP) have the microstructures describedabove.

However, Examples 1 and 2 display a “unique” sheet structure also. Theycontain a few sheets which are 0.02 to 0.1 microns thick and about 5-10microns long.

Example 20 Physical Properties of the Dried/calcined Powders Made fromSodium Silicate Under Mixing with Shear

The range of the key physical properties achieved with theabove-described methods of the present invention described in Examples1-17 were measured as:

(1) surface areas from 150 to 600 m²/gm;

(2) mean mesopore diameter (MMPD) from 60 to about 250 Å;

(3) varying modality of the pore size distribution from mono-modal tomulti-modal;

(4) measured pore volume (N₂) from 0.5 to 1.5 cc/gm;

(5) macropore volumes (Hg) up to 0.5 cc/gm;

(6) median particle size from 7 to 63 microns; and

(7) fragmentation potential from about 20 to about 30.

Example 21 TEM Characterization of SiO₂ Bases

The microstructure of SiO₂ base samples was evaluated with respect to:

(a) the presence of pockets of different densities in the matrix;

(b) the density of packing in the matrix; and

(c) the presence of sheet structures.

Specifically, the typical sizes of the pores in the pockets and in thematrix were estimated. An assessment of whether there were truemacropores was also made. As a comparison to the SiO₂ bases of thisinvention, experimental SiO₂ bases (e.g., 1936-20-13) made fromcommercially available dispersions and commercial SiO₂ bases (EP-30x andEP-50) were also examined.

The comparison results are summarized in Tables 2, 2A and 3. EM 2829(1936-20-13) (FIG. 3) clearly showed that the experimental SiO₂ basemade from silica dispersion was made up of particulates, while EM 3309(EP-50) (FIG. 4) showed that the matrix of EP-50 was made up of acontinuous network. For EP-30x, its matrix was made up of mostlyindividual particulates. However, the shape and size of theseparticulates were not as homogeneous as those in 1936-20-13. In someareas, the particulates appeared to be partially sintered and resembledthe continuous network. The matrices of all of the examples in thisinvention were made up of continuous networks. In addition, they allcontained pockets where the density of packing was lower than thesurrounding matrix. The number density of the pockets in the matrix(frequency of occurrence), the size of the pockets, and the porosity ofthe pockets were evaluated in a numerical relative ranking from 1 to 5.It should be noted that the ranking scale was neither linear norproportional. It only served to indicate an observable relativedifference. Furthermore, sheet structures were observed in the Examples1 and 2 samples 1935-23A and 1935-23B. A photomicrograph of Example 21935-23B, EM 3821, is included as FIG. 5. The true macropores weretypically located in the pockets. They can be recognized as empty spacesin the silica framework in the low magnification images.

The difference in the effects between aging in acid and aging in basewas clearly observed and illustrated by comparing Example 1935-44B (EM3735) (FIG. 6), Example 1935-47B (EM 3728) (FIG. 7), and Example1935-48B (EM 3743) (FIG. 8). Aging in acid did not change themicrostructure of the matrix but increased the pore size in the pocketsslightly. Aging in base increased the pore sizes significantly in boththe matrix and the pockets.

Example 22 Batch Reactor Evaluation of Large Pore Silica Catalyst Bases

Three experimental catalysts were evaluated for their reactivity(activity compared to a Benchmark EP-30X 1.0% chromium catalyst) atconstant ethylene maximum consumption, temperature, reactor volume,heptane addition, agitation via stirring, ethylene pressure, andaluminum to chrome ratio. The catalysts were activated at either 600° C.or 800° C. as indicated in Table 5 below which summarizes the reactorresults. EP-30X, a commercial catalyst discussed above in Example 21,was the benchmark catalyst. The experimental catalysts 1935-48B (acatalyst of the present invention discussed above in Example 21),1935-44 (a catalyst of the present invention also discussed above inExample 21), 1934-44 (also a catalyst of the present invention) werecompared to it. The activity of the catalyst on a gram of polymer pergram of chromium varied with the catalyst.

The catalyst activations were performed on a bench-scale 28 mm diameterfluidized bed under a stream of dry air at either 600° C. or 800° C. for8 hours. The activator tube is constructed from a 28 mm diameter quartzfrit, and a 67 mm diameter quartz disengaging section. The fluidizationsection is 300 mm long from the frit to the half angle transition, andthe disengaging section is 400 mm tall. The transition incorporates an11° half angle for ideal transition in fluidized bed design. The wholeactivator tube is enclosed in a Lindberg furnace and can be purged withargon or low dew point air, typically ˜1 L/minute. Gas flow direction isfrom the bottom to the top, and a cyclone trap is connected to theoutlet to collect fines, which might otherwise escape into theatmosphere. This scaled-down activation protocol mirrors that used inthe 4″ and 6″ activators at the Orange, TX, pilot plant.¹

Polymerizations were performed in 2 L autoclave reactors equipped withGenesis control systems. A dried 316ss 2 L Autoclave EngineersZipperclave reactor system is heated at 80° C. in-vacuo until a pressureof <50 mtorr is achieved. The reactor is then charged with a solution of0.2885 M 0.65 IBAO in 100 ml of heptane and a slurry of experimentalcatalyst in 100 ml heptane. The IBAO and catalyst amounts vary in μL andgrams respectively to give an Al to Cr proportion of 8.4 indicated inTable 5 below. The IBAO solution and Catalyst slurry were contained in a500 ml glass addition funnel that is fitted with a Kontes vacuum valve.The Kontes valve is connected to the reactor on a Cajon Ultra-Torrfitting, and the mixture is introduced into the reactor in-vacuo. Thereactor is stirred at 550 rpm and ethylene is introduced to an internalsetpoint pressure of 300 psi. The reactor temperature is maintained atthe setpoint temperature of 80° C. with a Neslab RTE-100 silicone orwater-bath circulator. The reactor is allowed to proceed to a givenproductivity, typically depletion of 80 L of ethylene, after which thereactor is vented and purged three times with argon and shut down. Thereactor is opened while it is still hot and the contents are quicklyremoved. The reactor is cleaned and prepared for the next reaction.¹

¹ The description of the activation technique and batch reactor setupand conditions are similar to previous work completed by Ed Vega forPamela Auburn and Theresa Pecoraro in “Alpo Catalyst Batch ScreeningStudies”, April 1994 and are reprinted here with permission from PamelaAuburn. Referring to Table 5, it can be seen that activity of theexperimental catalysts are superior to the commercial benchmark.

TABLE 5 Experimental Batch Reactor Runs for Large Pore Silicas IBAOPolymer Run Run Prior Activation Weight co-cat. Catalyst Al/Cr YieldTime Liter C₂ = Activity Activity Reactivity Sample ID number oxidation(degrees C.) % Cr soln. (μl) (g) ratio (g) (hr) consumed (g/g/hr)(g/mol/hr) EP30X  8 III 800 1.0 590 0.150 5.9 109.16 1.15 80.10 632.826.5 1.0 EP30X 15 III 800 1.0 590 0.150 5.9 114.03 1.07 80.10 710.5 29.81.1 C1935-48 16 III 600 1.0 700 0.125 8.4 108.30 0.76 81.68 1140.0 39.11.8 MEOH C1934-44 22 III 600 1.0 700 0.125 8.4 95.17 0.67 80.64 1136.439.5 1.8 MEOH C1935-44 H₂O 23 III 600 1.0 700 0.126 8.3 180.27 0.8896.40 1625.8 47.6 2.6 Constants: 80 L C₂ = consumption 2 L reactionvessel 80 degree Celsius reaction vessel 300 psi initial C₂ = addition5500 rpm agitation via stirring 200 ml heptane (100 ml soln w/ IBAO and100 ml slurry w/ catalyst) 0.2885 molar IBAO co-catalyst standardsolution

Gelling Mixed Silica-oxide Salts

It is also possible to form gels from an acidic mixture of oxideprecursors and a sodium silicate plus acid by adding a base such asammonium hydroxide. In this case the acidic solution contained both asilica and an alumina precursor. The basic solution was ammoniumhydroxide. The acid and base solutions were mixed with high-shear,continuous gelation (CHSG) using a two-stream feed system pumpeddirectly into a Ross mixer (reactor) as described above. This resultingsilica-alumina contained a unique sheet-like structure.

Example 23 Procedure for Preparing SiAl of Prior Art

The following is a description of the procedure by which Example1252-36B, a conventional silica alumina, 60:40 wt ratio, was prepared.Some of the process steps described below were used to prepare thesilica-alumina samples of the present invention.. The difference wasthat the materials of the present invention were prepared in thepresence of mixing with shear forces.

I - Starting Materials Material Source Key Concentration AluminumChloride 32 BE Reheis 10.8% Al₂O₃ Glacial Acetic Acid JT Baker 99.9%Sodium Silicate 41 BE VWR 40% w/v Sodium Silicate Ammonium AcetateSolution Amresco Inc. 65% solution

II—Gelation

1. Add 22.2 lb. of DI water to a 55-gallon tank and turn on the mixer(Nettco Model NSP 050 mixer).

2. Add 53.92 lb. of aluminum chloride solution to the DI water.

3. Add 4.05 lb. of acetic acid to the aluminum chloride solution andrecord the pH. It should be <0.

4. In a separate tank make up a sodium silicate solution by mixing 23.34lb. of sodium silicate with 126.4 lb. of DI water. Record the pH. Itshould be around 12.

5. Pump the sodium silicate solution into the aluminum chloride solutionat approximately 5 lb./min. with a Masterflex magnetic drive vein pump.NOTE: If the silicate solution is added too quickly, it may come out ofsolution. The resulting solution should be clear. Measure and record thepH. It should be around 2.8.

6. Make up a solution of ammonium hydroxide which is 1 part NH₄OH and3.205 parts DI water w/w. It will take approximately 90 lb. of theammonium hydroxide solution to do the titration. Make an excess ofammonium hydroxide. Record the pH.

7. Begin the titration by pumping the ammonium hydroxide solution intothe acid solution (from step 3) at 918 ml per minute. Titrate to a pH of8.0. The titration was done in a 100-gallon tank using a Lightnin ModelXD-43 mixer running at about 1788 RPM.

The following titration table is typical:

Time min. Base Added lb. pH  0 0 2.8  7 9.2 3.06 19 23.1 3.42 35 42.73.92 56 64.8 4.9 66 75 6 72 81.6 8 80 89.1 8.03

8. At the end of the titration, add ammonium hydroxide as necessary tomaintain a pH of 8.0 for 3 hours. It should take about 1.6 lb. of baseover 3 hours to keep the pH at 8.0. The pH will drift the most duringthe first hour. After 2 hours, the pH should be fairly stable.

9. At the end of three hours, begin washing the gel-slurry.

III—Quenching: Not applicable.

IV—Washing: Difiltration

The gel-slurry was washed with an ammonium acetate solution consistingof 1.8 liters of 65% ammonium acetate solution in approximately 55gallons of DI water followed by a DI water wash. Used New Logic's V*SEPdifiltration equipment.

On day one, the gel was washed with 256 liters of acetate solution forone hour. The conductivity went from 51,300 mmhos to 29,000 mmhos. Thenext day, the gel was washed with 398 liters of the acetate solutionover 2 hours. The conductivity decreased to 11,000 mmhos. At 11,000mmhos, the wash liquid was changed to DI water. The gel was washed with719 liters of DI water over 4.5 hours to a conductivity of 958 mmhos. Onday three, the wash continued using 183 liters of DI water over 1 hourto decrease the conductivity to the target of 600 mmhos.

Acidification/Concentration

The gel-slurry was acidified in a 20-gallon tank with mixing by an airdriven mixer with a marine impeller. Approximately half of the slurrywas acidified to a pH of 5.6 with 96.3 grams of acetic acid. The acidwas added in two increments of 71.3 and 25 grams. The first acidaddition was dumped in all at once. The second addition was added slowlyuntil the pH reached 5.6.

The acidification process takes about 20-30 minutes. During that time,the gel is being de-watered. Once a stable pH of 5.6 is reached, thedewatering goes on for another 5-10 minutes before the gel gets toothick to pump out of the mixing tank. The final concentration was 8.6%solids by LOM.

The other half of the gel-slurry was acidified the following day to a pHof 5.6 with 106 grams of acetic acid. The acid was added in incrementsof 35.5 g, 28.3 g and 42.2 g. The first two acid additions were dumpedin all at once. The last addition was added slowly until the pH reached5.6.

Again, the gel-slurry was dewatered during the process to a finalconcentration of 8.6% solids by LOM.

V—Aging: None.

VI—Spray Drying

The slurry was spray dried separately with a Stork Bowen Model BE 1235Spray Dryer.

Calcination

The powder was calcined in air in a fixed fluidized bed reactor. Thecalcination is an automated process which follows the following program:

Program

15 minute ramp to 213° F. 1 hour hold.

20 minute ramp to 482° F. 1 hour hold.

20 minute ramp to 762° F. 1 hour hold.

20 minute ramp to 1100° F. 2 hour hold.

Cool to room temperature.

Table 6 summarizes the key process variables and the resulting physicalproperties of the formed and calcined silica alumina powders resultingfrom the CHSG experiments. Example 23 represents the prior art. Examples24 and 25 represent material of this invention, 1934-45 and 1935-13AF.Tables 7 and 8 summarize the observations associated with each of theCHSG, continuous, high shear, experiments.

Example 24 This Invention

The same starting materials were used as above.

26.96 lbs of AlCl₃ solution was added to 14.4 lbs of DI water. Theacetic acid, 918 grams, was added to the aluminum solution. The pH wasless than zero. 11.18 lbs of the sodium silicate was added to 63.2 lbsof DI water with mixing. The silicate solution was pumped into thealuminum-acetic acid solution over a period of fifteen minutes withmixing. The pH was about 2.3. An ammonium hydroxide: Di water solutionwas prepared by a 1 3.205 w/w dilution. The pH was 11.6. The acid andthe base solutions were pumped into the Ross high-shear mixer-reactor.The specifics are summarized in Table 6. The gel from the reactor wascollected in a tank of DI water with mixing. Acetic acid was added tokeep the pH at 8.0. The pH was maintained at 8.0 for one hour beforewashing.

The remaining process steps were similar to Example 23. Table 6 containsthe specifics.

Example 25: This Invention

The same starting materials were used as above.

26.96 lbs. of AlCl₃ solution was added to 16.69 lbs of DI water. Theacetic acid, 918 grams, was added to the aluminum solution. The pH wasless than zero. 11.18 lbs of the sodium silicate was added to 63.2 lbsof DI water with mixing. The silicate solution was pumped into thealuminum-acetic acid solution over a period of fifteen minutes withmixing. The pH was about 2.3. An ammonium hydroxide: DI water solutionwas prepared by a 1 to 3.205 w/w dilution. The acid and the basesolutions were pumped into the Ross high-shear mixer-reactor. Thespecifics are summarized in Table 6. The remaining process steps weresimilar to Example 23. Table 6 contains the specifics.

TABLE 6 Preparation Conditions for the Silica/Alumina Bases of thisInvention Prior Art This Invention Example No Comparative: 23 24 25Notebook No 1252-36B 1934-45 1935-13AF I) Solutions A) Al solution 32 BeAlCl₃, Lb. 53.92 26.96 26.96 Glacial Acetic Acid 4.05 2.025 2.025(99.9%), Lb DI H₂O, Lb 22.2 14.1 16.7 pH <0 <0 <0 B) Si SolutionNa₂O.SiO₂, 1:3.22, Lb 23.34 11.18 11.18 (Banco Sodium silicate, 41 Be)DI H₂O, Lb 126.4 63.2 63.2 pH 12 11.6 11.5 C) NH₄OH Solution NH₄OH:NH₄OH: NH₄OH: DI H₂O = DI H₂O = DI H₂O = 1:3.205 w/w 1:3.205 w/w 1:3.205w/w II) Gelation: High Shear No Yes Yes Stator configuration ScreenScreen RPM of Rotor 2785 2680 Apparent Average Shear 1.97 1.9 Rate(1), ×(10)⁴ pH Range 5 to 9 7.7 to 8.5 Acid Rate, gm/min 1947 to 2231 1468 to2793 Base Rate, gm/min  883 to 1016 420 to 690 pH at outlet 8.8 7.7 to8.5 Gel T, C. 26 28 III) Quench No Yes No IV) Washing Batch No No NoWash Solution pH of Wash Solution Wash Temperature, ° C. Conductivity ofWater Wash (1) Initial, mmhos/cm² (2) Final Wash Temperature, ° C.Dilution, Wt % Solids (LOM) Wash Solution NH₄ Acetate NH₄ Acetate NH₄Acetate pH of Wash Solution 7.3 7.3 Conductivity of Water Wash (1)Initial 11000 9000 12000 (2) Final 600 455 518 Wash Temperature, ° C.Ambient Ambient 50 Acidified, pH 5.6 5.6 5.62 Wt % Solids of 8.6 5.4 1to 7 Concentrate V) Aging No No No VI) Drying Spray Spray Spray DryingDrying Drying VII) Physical Properties (2) Surface Area (BET), 249 422319 to 340 m²/gm Pore Volume (BET) 0.865 0.527 0.524 to cc/gm 0.644MMPD, Å 173 81  96 to 105 Particle size, microns 94 30 9 (1) AASR =Apparent Average Shear Rate, reciprocal seconds (2) Measurement madeafter calcination for 2 hrs at 593° C., in a fixed fluidized bedreactor.

Example 26 TEM Characterization of Silica/Alumina Samples

The microstructure of the silica/alumina bases was evaluated withrespect to:

(a) the presence of pockets of different densities in the matrix;

(b) the density of packing in the matrix; and

(c) the presence of sheet structures.

Specifically, the microstructures of the samples of this inventionExamples 24 and 25 (for example, 1933-45 and 1934-13AF) were compared toa sample prepared without shear Example 23 (1252-36B). The typical sizesof the pores in the pockets and in the matrix were also estimated. Theresults are summarized in Tables 7 and 8 below. They showed that onlythe samples made by the CHSG method contained sheet structures. Thesesamples also have a much denser matrix framework. This is illustrated bycomparing EM 0331 (1252-36B) (FIG. 9) and EM 2269 (1934-45) (FIG. 10).

A Silica/Alumina catalyst base, Example 25 (C1935-13A) made by highshear continuous gelations was also analyzed.

The material contains the unique sheet structure discussed above. Thematerial is amorphous with no evidence of any kind of phase separation.

Tables 7 and 8 below summarize and compare the physical properties andTEM characteristics of Silica/Alumina bases of the present invention tothe prior art.

TABLE 7 Comparison of the Physical Properties and the Microstructure ofthe Si/Al Bases of This Invention to the Prior Art Prior Art ThisInvention Example Comparative:23 24 25 Sample Id 1252-36B 1934-451935-13AF Surface Area, m²/g 249 422 319 (BET) Pore Volume (N₂) 0.8650.527 0.524 Mean Meso Pore 173.4 81 90 Diameter XRD Amorphous AmorphousAmorphous “True” Macro PV (TEM) No Yes Yes Microstructures (TEM)Particulates No No No Continuous network X X X matrix Pockets X X XSheets No X X

TABLE 8 TEM Characterization of Silica/Alumina Bases of the Prior Artand of this Invention Prior Art This Invention 1252- 1934- 1935- SampleID 36B 45 13A Fines Example Comparative: 23 24 25 Amorphous Yes Yes YesParticulates No No No Size of Particulates Size of Pores Continuosnetwork matrix X X X Density of Matrix — — — Size of Matrix Pores, nm 50to 100 5 5 Pockets No X X Density of Pockets 5 5 (relative ranking) Sizeof Pockets, microns 2 to 5 5 Porosity of Pockets 4 4 (relative ranking)Size of Pocket Pores, 30 70 Typical, nm Size of Pocket Pores, 10 to 6030 to 500 Range, nm Sheets No X X Size of sheets Thickness, nm  20 to100 20 to 100 Length, microns 1 to 3 1 to 3 

While the present invention has been described with reference tospecific embodiments, this application is intended to cover thosevarious changes and substitutions that may be made by those skilled inthe art without departing from the spirit and scope of the appendedclaims.

What is claimed is:
 1. A method for preparing a silica gel compositionwhich is a precursor material for a silica powder material with amicrostructure comprising a non-particulate, dense, continuous, networkmatrix and encapsulated, less dense, non-particulate regions with truemacropores, the method comprising: (a) forming a first aqueous solutioncomprising silica ions; (b) forming a second aqueous solution capable ofneutralizing said first aqueous solution; and (c) contacting said firstand second aqueous solutions in a mixer-reactor under mixing conditionsat an apparent average shear rate greater that about 0.5×10⁴ sec⁻¹ toform the silica gel composition.
 2. The method according to claim 1further comprising aging the silica gel composition in acidic or basicconditions for up to one hour.
 3. The method of preparing the silicapowder composition from the silica gel composition prepared by themethod of claim 1, comprising the steps of: (a) washing the silica gelwith solutions of ammonium acetate, bicarbonate or nitrate; (b) washingthe silica gel composition in deionized water to further replacesalts-contaminated water in the composition with fresh water; and (c)drying the washed composition to remove substantially all water.
 4. Themethod of claim 3, further comprising calcining the dried compositionfor up to 8 hours at a maximum temperature of 450° C.
 5. The methodaccording to claim 1, wherein said first aqueous solution is an acidicsolution comprising sodium silicate and acid wherein the second aqueoussolution has a pH above
 8. 6. The method according to claim 1, whereinsaid second aqueous solution is an ammonia based material selected fromthe group consisting of ammonium hydroxide; ammonium carbonate; ammoniumbicarbonate and urea.
 7. The method according to claim 1, wherein saidfirst aqueous solution is a basic solution of sodium silicate andwherein the second aqueous solution has a pH below
 6. 8. The methodaccording to claim 1, wherein said second aqueous solution is sulfuricacid.
 9. The method according to claim 1, wherein said neutralizationstep is conducted in such a manner that the pH of the combined firstaqueous solution and the neutralizing medium is controlled in the rangeof about 3.5 to about
 11. 10. The method of claim 1, wherein saidcatalyst is activated by being heated to a temperature in the range of300° C. to 900° C. for from 2 to 16 hours.
 11. The method of claim 5further comprising the steps of: (a) preparing an aqueous slurry ofamorphous silica gel by continuously feeding an acidic solutioncomprising sodium silicate and acid to an emulsifier mixer whilesimultaneously and continuously feeding to said mixer an alkalinesolution; (b) operating said mixer at an apparent average shear rategreater the about 0.5×10⁴ sec⁻¹ so that the precipitated silicate hassheets of silica in its microstructure; (c) recovering said silica fromsaid aqueous slurry using a vibrating filtration membrane to a solidscontent from 8 to 20 wt. %, after washing; (d) drying the silica from(c); (e) calcining the silica from (d); (f) dispensing a chromiumcompound substantially uniformly onto said silica from (d) or (e) toform a catalyst having from 0.01 to 4 wt. % chromium; (g) drying saidcatalyst; and (h) activating said dry catalyst from (f) by heating to atemperature from 300° C. to 900° C. for from 2 to 16 hours.
 12. A methodfor preparing silica alumina powder material with a microstructurecomprising a non-particulate, dense continuous network matrix,encapsulated regions with true macropores, and sheets, the methodcomprising: (a) preparing an acid aqueous solution comprising aluminumand silicon ions; (b) preparing a basic aqueous solution comprisingammonium hydroxide; (c) mixing the acidic aqueous solution and the basicaqueous solution in a mixer at an apparent average shear rate graterthan about 0.5×10⁴ sec⁻¹ to obtain a gel slurry with a microstructurecomprising a non-particulate, dense, continuous network matrix,encapsulated regions with true macropores and sheets; (d) maintainingthe gel slurry at approximately pH 8.0 for up to one hour before washingthe gel; (e) washing the gel slurry first with aqueous acetate solution,then with water to obtain a gel conductivity below 1,000 mmhos; (f)acidifying and concentrating the gel slurry by adding acid to the gelslurry to achieve a pH below 6.0 while gradually removing water from thegel slurry; and (g) drying and calcining the gel slurry to form thesilica-alumina powder material.